Not applicable
Organic light emitting devices (OLEDs) are comprised of several thin layers of organic materials. These layers can be made to electroluminesce by applying a voltage across the device, and with sufficient brightness, range of color and operating lifetimes can be a practical alternative to LCD-based full color flat-panel displays. By placing red (R), green (G), and blue (B) emitting organic materials in a vertically stacked geometry with other transparent thin organic films, a new OLED display pixel is achieved which can be fabricated simply and provide a cost effective display panel.
In general, these OLED devices rely on a common mechanism leading to optical emission. Typically, this mechanism is based upon the radiative recombination of a trapped charge. Specifically, OLEDs will contain at least two thin organic layers separating the anode and cathode of the device. The material of one of these layers is specifically chosen based on the material""s ability to transport holes, a xe2x80x9chole transporting layerxe2x80x9d (HTL), and the material of the other layer is specifically selected according to its ability to transport electrons, an xe2x80x9celectron transporting layerxe2x80x9d (ETL). With such a construction, the device can be viewed as a diode with a forward bias when the potential applied to the anode is higher than the potential applied to the cathode. Under these bias conditions, the anode injects holes (positive charge carriers) into the hole transporting layer, while the cathode injects electrons into the electron transporting layer. The portion of the luminescent medium adjacent to the anode thus forms a hole injecting and transporting zone while the portion of the luminescent medium adjacent to the cathode forms an electron injecting and transporting zone. The injected holes and electrons each migrate toward the oppositely charged electrode. When an electron and hole localize on the same molecule, a Frenkel exciton is formed. Recombination of this short-lived state may be visualized as an electron dropping from its conduction potential to a valence band, with relaxation occurring, under certain conditions, preferentially via a photoemissive mechanism. Under this view of the mechanism of operation of typical thin-layer organic devices, the electroluminescent layer comprises a luminescence zone receiving mobile charge carriers (electrons and holes) from each electrode.
The materials that function as the electron transporting layer of the OLED are frequently the same materials that are incorporated into the OLED to produce the electroluminescent emission. Such devices in which the electron transporting layer functions as the emissive layer are referred to as having a single heterostructure. Alternatively, the electroluminescent material may be present in a separate emissive layer between the hole transporting layer and the electron transporting layer in what is referred to as a double heterostructure.
In addition to emissive materials that are present as the predominant component in the electron transporting layer, and that function both as the electron transporting material as well as the emissive material, the emissive material may itself be present in relatively low concentrations as a dopant in the electron transporting layer. Whenever a dopant is present, the predominant material in the electron transporting layer may be referred to as a host material. Materials that are present as host and dopant are selected so as to have a high level of energy transfer from the host to the dopant material. In addition, these materials need to be capable of producing acceptable electrical properties for the OLED. Furthermore, such host and dopant materials are preferably capable of being incorporated into the OLED using starting materials that can be readily incorporated into the OLED by using convenient fabrication techniques, in particular, by using vacuum-deposition techniques.
It is desirable for OLEDs to be fabricated using materials that provide electroluminescent emission in a relatively narrow band centered near selected spectral regions, which correspond to one of the three primary colors, red, green and blue so that they may be used as a colored layer in an OLED or stacked OLED. Additionally, the compounds should come from a class of compounds in which the emission may be varied by selectively varying the substituents or by modifying the structure of a base compound that produces emission from a charge transfer transition. Still further, the compounds should be capable of being readily deposited as a thin layer using vapor-phase or vacuum deposition techniques so that the compound can be readily incorporated into an OLED that is prepared entirely from, for example, vacuum-deposited organic materials. Still other considerations for new OEL materials involves considerations of environmental stability, cycle life and ease of fabrication. In order to ensure environmental stability and long cycle life, the organic phosphors should be as inert to unwanted chemical and electrochemical reactions as possible.
A candidate structure in terms of stability would be polyparaphenylene (PPP), a polymer composed of a sequence of linearly connected benzene rings. PPP has excellent stability and luminescence properties, but is neither soluble in organic solvents nor volatile. As a result, PPP cannot be deposited as a thin film on a substrate surface to allow fabrication of a useful display device.
What is needed in the art are new polyparaphenylene materials that have suitable solubility and or deposition properties and further have the desired luminescence properties. Surprisingly, the present invention provides such compounds.
In one aspect, the present invention provides an oligomeric para-phenylene compound having the formula:
R1xe2x80x94(Ari)nxe2x80x94R2
wherein the subscript n is an integer of from 5 to 15; the superscript i is an integer of from 1 to n and denotes the position downstream from R1; each Ari is a substituted or unsubstituted aryl group; R1 and R2 are each substituents that increase the solubility of the para-phenylene compound in nonpolar organic solvents relative to the solubility of the corresponding compound wherein R1 and R2 are hydrogen; with the proviso that the Ari groups are linked together in a 1,4-paraphenylene manner.
Preferably the substituents R1 and R2 each independently have the formula:
R3xe2x80x94(Arj)mxe2x80x94
wherein the subscript m is an integer of from 1 to 5; the superscript j is an integer of from 1 to m and denotes the position of each Arj away from R3. Each Arj is selected from:
a) a 1,4-phenylene group having the formula: 
wherein each R4 is independently selected from H, substituted or unsubstituted (C1-C12)alkyl, substituted or unsubstituted (C1-C12)alkoxy, substituted or unsubstituted (C1-C12)alkylamino, substituted or unsubstituted (C1-C12)alkylthio, substituted or unsubstituted di(C1-C12) alkylamino, substituted or unsubstituted arylamino, substituted or unsubstituted diarylamino and halogen, with the proviso that at least two of the four R4 substituents are independently selected from substituted or unsubstituted (C1-C12)alkyl and substituted or unsubstituted (C1-C12)alkoxy, and
b) an aryl biradical selected from 1,4-naphthylene, 1,4-anthrylene, 9,10-anthrylene, 5,6,7,8-tetrahydronaphth-1,4-ylene, 9,9xe2x80x2,10,10xe2x80x2-tetra(C1-C12)alkyl-9,10-dihydroanthr-1,4-ylene, 9,9xe2x80x210,10xe2x80x2-tetraaryl-9,10-dihydroanthr-1,4-ylene, 9,9xe2x80x210,10xe2x80x2-tetra(C1-C12)alkyl-9,10-dihydroanthr-2,6-ylene, and 9,9xe2x80x210,10xe2x80x2-tetraaryl-9,10-dihydroanthr-1,4-ylene; and R3 is selected from H, substituted or unsubstituted (C1-C12)alkyl, substituted or unsubstituted (C1-C12)alkoxy, substituted or unsubstituted (C1-C12)alkylamino, substituted or unsubstituted (C1-C12)alkylthio, substituted or unsubstituted di(C1-C12)alkylamino, substituted or unsubstituted arylamino, substituted or unsubstituted diarylamino and halogen.
In another aspect, the present invention provides a polymer of the formula:
R11xe2x80x94(Qi)pxe2x80x94R12
wherein each R11 and R12 is independently selected from H, substituted or unsubstituted (C1-C12)alkyl, substituted or unsubstituted (C1-C12)alkoxy, substituted or unsubstituted (C1-C12)alkylamino, substituted or unsubstituted (C1-C12)alkylthio, substituted or unsubstituted di(C1-C12)alkylamino, substituted or unsubstituted arylamino, substituted or unsubstituted diarylamino and halogen; the subscript p is an integer of from 5 to 200; the superscript i is an integer of from 1 to p and indicates the position downstream from R1 of each Q; each Qi is a benzoquinone or hydroquinone subunit selected from the formulae: 
wherein each X is independently selected from H, substituted or unsubstituted (C1-C12)alkyl, substituted or unsubstituted (C1-C12)alkoxy, substituted or unsubstituted (C1-C12)alkylamino, substituted or unsubstituted (C1-C12)alkylthio, substituted or unsubstituted di(C1-C12)alkylamino, substituted or unsubstituted arylamino, substituted or unsubstituted diarylamino and halogen.
In one group of embodiments, the hydroquinone and benzoquinone subunits are present in about a 50:50 ratio. In another group of embodiments, the hydroquinone and benzoquinone subunits alternate in the polymer so that no two hydroquinone subunits are adjacent and no two benzoquinone subunits are adjacent. In yet another group of embodiments, two adjacent hydroquinone subunits alternate with one benzoquinone subunit. In still another group of embodiments, two adjacent benzoquinone subunits alternate with one hydroquinone subunit.
In yet another aspect, the invention provides a block copolymer having the formula:
R21xe2x80x94(Qj)kxe2x80x94R22
wherein each R21 and R22 is independently selected from H, substituted or unsubstituted (C1-C12)alkyl, substituted or unsubstituted (C1-C12)alkoxy, substituted or unsubstituted (C1-C12)alkylamino, substituted or unsubstituted (C1-C12)alkylthio, substituted or unsubstituted di(C1-C12)alkylamino, substituted or unsubstituted arylamino, substituted or unsubstituted diarylamino and halogen; the subscript k is an integer of from 2 to 20; the superscript j is an integer of from 1 to k and indicates the position downstream from R2l of each Q; each Qj is a para-phenylene block subunit (e.g., xe2x80x94(Ari)nxe2x80x94) or a solubility-enhancing subunit (e.g, xe2x80x94(Arj)mxe2x80x94) wherein the subscript n is an integer of from 5 to 15; the superscript i is an integer from 1 to n; the subscript m is an integer of from 1 to 5; the superscript j is an integer from 1 to m; each Ari is a substituted or unsubstituted aryl group linked in a manner that maintains a coplanar orientation relative to adjacent Ari groups; each Aij is selected from
a) a 1,4-phenylene group having the formula: 
wherein each R23 is a member independently selected from H, substituted or unsubstituted (C1-C12)alkyl, substituted or unsubstituted (C1-C12)alkoxy, substituted or unsubstituted (C1-C12)alkylamino, substituted or unsubstituted (C1-C12)alkylthio, substituted or unsubstituted di(C1-C12)alkylamino, substituted or unsubstituted arylamino, substituted or unsubstituted diarylamino and halogen, with the proviso that at least two of the four R23 substituents are independently selected from substituted or unsubstituted (C1-C12)alkyl and substituted or unsubstituted (C1-C12)alkoxy, and
b) an aryl biradical selected from 1,4-naphthylene, 1,4-anthrylene, 9,10-anthrylene, 5,6,7,8-tetrahydronaphth-1,4-ylene, 9,9xe2x80x2,10,10xe2x80x2-tetra(C1-C12)alkyl-9,10-dihydroanthr-1,4-ylene, 9,9xe2x80x210,10xe2x80x2-tetraaryl-9,10-dihydroanthr-1,4-ylene, 9,9xe2x80x210,10xe2x80x2-tetra(C1-C12)alkyl-9,10-dihydroanthr-2,6-ylene, and 9,9xe2x80x210,10xe2x80x2-tetraaryl-9,10-dihydroanthr-1,4-ylene.
In one group of preferred embodiments, Q1, Q3 and Q5 are block para-phenylene subunits and Q2, Q4 and Q6 are solubility enhancing subunits. In another group of preferred embodiments, Q1, Q3, Q5 and Q7 are solubility enhancing subunits and Q2, Q4 and Q6 are block para-phenylene subunits.
In still another aspect, the present invention provides a branched polymeric aromatic compound having the formula: 
wherein each R is selected from substituted or unsubstituted (C1-C12)alkyl, substituted or unsubstituted (C1-C12)alkoxy, phenyl and halogen; the subscript n is an integer of from 3 to 8; the superscript i is an integer of from 1 to n and denotes the positions of each Ar away from the central tetrasubstituted phenyl ring; and each Ari is a substituted or unsubstituted aryl group that can be the same or different from Ari at any other position; with the provisos that the Ari groups are linked together in a 1,4-paraphenylene manner.
In still another aspect, the present invention provides a method of preparing a polymeric OLED material on a solid support, the method comprising:
(a) contacting a solid support-bound aryl diazonium salt with 3,6-dichloroquinone under conditions sufficient to form a solid support-bound aryl quinone derivative; and
(b) contacting the solid support-bound aryl quinone derivative with a diazonium compound having the formula: 
wherein each X1 is a blocking group and the subscript n is an integer of from 0 to 4; under conditions sufficient to form an intermediate poly OLED material;
(c) repeating steps (a) and (b) from 2 to 70 times; and
(d) contacting the product of step (c) with a terminating diazonium compound having the formula: 
wherein each X2 is a blocking group, R is selected from H, substituted or unsubstituted (C1-C12)alkyl, substituted or unsubstituted (C1-C12)alkoxy, substituted or unsubstituted (C1-C12)alkylamino, substituted or unsubstituted (C1-C12)alkylthio, substituted or unsubstituted di(C1-C12)alkylamino, substituted or unsubstituted arylamino and substituted or unsubstituted diarylamino; and m is an integer of from 0 to 4.
In one group of embodiments, an intermediate poly OLED material is produced having the formula: 
wherein L is a linking group; the shaded sphere is a solid support; and X1 is a member selected from halogen, substituted or unsubstituted (C1-C12)alkyl, substituted or unsubstituted (C1-C12)alkoxy, substituted or unsubstituted (C1-C12)alkylamino, substituted or unsubstituted (C1-C12)alkylthio, and substituted or unsubstituted di(C1-C12)alkylamino. Preferably, the solid support is selected from glass, tin oxide, indium oxide, and mixtures thereof.
In yet another aspect, the present invention provides a solid support-bound poly OLED material formed by the methods above.
In another aspect, the present invention provides a polyfurano ladder oligomer having the formula: 
wherein the subscript z is an integer of from 2 to 7; each of R31, R32, R33, R34, R35, R36 is independently selected from H, substituted or unsubstituted (C1-C12)alkyl, substituted or unsubstituted (C1-C12)alkoxy and halogen. Preferably, R32 and R35 are each H. More preferably, z is an integer of from 2 to 4; and R32 and R35 are each H. Methods of preparing the polyfurano ladder oligomers by photoreaction of an appropriate precursor are also provided.
In another aspect, the present invention provides a method of forming a light emitting polymer, the method comprising exposing an oligomeric para-phenylene compound of claim 1 having attached acrylate ester groups to sufficient ultraviolet light to form a light emitting polymer comprising a plurality of oligomeric para-phenylene compounds covalently attached to each other via ester and ether linkages.
In yet another aspect, the present invention provides a method of forming a light emitting polymer, the method comprising exposing a polyfurano ladder oligomer having attached acrylate ester groups to sufficient ultraviolet light to form a light emitting polymer comprising a plurality of said polyfurano ladder oligomers covalently attached to each other via ester and ether linkages.